Objective Measurements of Ossicular Chain Mobility Using a Palpating Instrument Intraoperatively

The judgment of a normal or impaired mobility of middle ear ossicles is based on palpation and depends highly on the surgeon's subjective experience. The aim of this study was to develop and test a palpating instrument recording force and vector and allowing to support the surgeon's subjective impression with objective measurement results.

Prospective recordings at surgery.

Tertiary referral center.

A fiberoptic force-sensing element allowing force measures in three orthogonal directions was integrated into a handheld 45 degree hook and tested in temporal bones. Clinical data series from patients with a functionally normal chain (e.g., cochlear implants (CI)) and impaired ossicles (otosclerosis) were collected. The ossicles were palpated until their first movements out of the resting stage were visualized, the applied force, and vector were recorded by an independent observer.

Four CI and 19 otosclerosis patients were further evaluated. The minimum detectable force change of the sensor was 0.2 gF (2 mN). In the otosclerosis patients the average force applied to move the malleus was 9.5 gF, on the incus 8.7 gF. These values were slightly lower after separation of the incudostapedial joint, reaching 8.5 gF and 6.9 gF, respectively. The fixed stapes showed a rigidity of 14.7 gF or higher. The values were lower in the CI group measuring 4.4 gF, 4.1 gF, and 3.3 gF on the three ossicles, respectively.

We were able to produce a disposable, easy-to-handle palpating probe that enables the otologist to record continuously tip contact forces in three dimensions during his standard palpation of each ossicle. Normative values were reproduced for each ossicle, as well as increased rates for stapes fixation in otosclerosis.